The overall purpose of this monograph is to provide a logical, comprehensive, and economical framework for the discussion, instruction, and research related to polygraph countermeasures. A polygraph “countermeasure” is defined as “any method used with the intent of precluding a correct polygraph outcome.” The taxonomy of countermeasures presented is based on two criteria: countermeasures that use mechanisms in common are grouped together; and the groupings are based solely on the primary characteristics of the countermeasure. Based on these two criteria, the body of literature on this subject suggests that all polygraph countermeasures can be grouped into four categories: physical countermeasures, mental countermeasures, pharmacological/chemical countermeasures, and behavioral countermeasures. This monograph is organized into sections that correspond to these classes. Within each section, definitions of the features of these countermeasures are provided, along with examples. The relevant research is also reviewed; and where appropriate, ways to counter the countermeasures are proposed. 62 references